1. Field of the Invention
The present invention relates broadly to systems and methods for managing electric brakes in trailers or other towed vehicles. More particularly, the present invention concerns a system and method for managing an electric brake in a trailer or other towed vehicle during a breakaway event, in which the towed vehicle separates from a towing vehicle, by controlling or managing current flow or delivery to the electric brake so as to maximize both effectiveness and efficiency.
2. Description of the Prior Art
It is necessary, during a breakaway event in which a trailer or other towed vehicle unexpectedly and unsafely separates of xe2x80x9cbreaks awayxe2x80x9d from a towing vehicle, to manage the operation and application of the trailer""s electric brakes so as to safely stop the trailer. The trailer typically includes a first or front electric brake and a second or rear electric brake, operation of which is slaved to or otherwise controlled by the towing vehicle under normal conditions. During a breakaway event, however, separation of the vehicles interrupts communication between them, making an independent emergency braking system necessary in order to stop the trailer.
In the prior art, an emergency braking system typically includes a breakaway switch assembly and a trailer-mounted battery. The breakaway switch assembly includes a mechanical switch; a plunger to activate the mechanical switch; and a cable mechanically connecting the plunger to the towing vehicle. Separation of the trailer from the towing vehicle causes the cable to actuate the plunger which, in turn, causes the switch to electrically connect the battery directly to the first and second electric brakes. The battery then delivers maximum electric current to the electric brakes until either the switch is manually deactivated or reset or the battery is completely discharged. Under current Federal Department of Transportation regulations, the emergency braking system must provide for applying the electric brakes for a period of not less than fifteen minutes following activation.
Unfortunately, the prior art emergency braking system suffers from a number of serious limitations and disadvantages, including, for example, that delivering maximum current can reduce the effectiveness of the electric brakes by causing them to lock, thereby causing the wheels to skid and reducing traction. Furthermore, once the trailer has stopped, it becomes an unnecessary and inefficient waste of current to continue to deliver maximum current to the electric brakes for the remainder of the requisite fifteen minute period because maximum current is not necessary to hold or maintain the stopped trailer in place. Additionally, maximum power is typically delivered to both the first and second electric brakes for the entire fifteen minute period, even though both electric brakes are not necessary to hold the stopped trailer in place. Thus, in the prior art emergency braking system, maximum braking is applied throughout the requisite fifteen minute period, even though maximum braking may not provide maximum braking effectiveness while the trailer is moving and may not provide maximum power-use efficiency once the trailer has stopped. Those with ordinary skill in the electrical arts will appreciate that delivering maximum current to both the first and second electric brakes for fifteen continuous minutes requires that the trailer battery be relatively large, heavy, and expensive in order to have sufficient charge capacity.
Due to these problems and limitations in the prior art, an improved emergency braking system is needed that provides both improved effectiveness and improved efficiency.
The present invention overcomes the above-identified problems and limitations in the prior art with an emergency braking system and method for managing an electric brake in a trailer or other towed vehicle during a breakaway event by controlling or managing current flow or delivery to the electric brake so as to maximize both effectiveness and efficiency. Though described as being used with a trailer having both a first or front electric brake and a second or rear electric brake and a trailer-mounted battery, the system may be used in virtually any type of towed vehicle having any number and configuration of electric brakes or electric current sources.
In a preferred embodiment, the system broadly comprises a breakaway switch assembly and a power management module. The breakaway switch assembly provides a signal indicating occurrence of a breakaway event. In one possible implementation, the breakaway switch assembly may be substantially similar or identical in form to the breakaway switch assemblies of prior art emergency braking systems. Thus, the breakaway switch assembly may include a mechanical switch; a plunger to actuate the mechanical switch; and a cable mechanically connecting the plunger to the towing vehicle. As in prior art systems, separation of the towing and towed vehicles pulls the cable and removes the plunger to actuate the switch. In contrast to the prior art systems, however, actuation of the switch does not directly electrically connect the battery to the electric brakes to deliver maximum current in a substantially unrestricted and uncontrolled manner.
The power management module is interposed between the battery and the electric brakes and is adapted to manage or control current flow or delivery to the electric brakes so as to achieve both improved effectiveness and improved efficiency. More specifically, the power management module functions to deliver a first level of current for a first duration or initial portion of the fifteen minute period in order to stop the trailer, and then deliver a second level of current for a second duration or remaining portion of the fifteen minute period to hold or maintain the stopped trailer in place.
The first and second levels of current may be of substantially fixed, pre-established magnitudes and the first and second durations may be of substantially fixed, pre-established durations. Alternatively, the first and second levels of current may be of substantially variable magnitudes and the first and second durations may be of substantially variable lengths so as to allow for actively adapting the braking action to specific circumstances of the breakaway event. In order to facilitate such active adaptation, the system may include one or more sensors operable to determine and communicate to the power management module information related to, for example, whether the first or second electric brakes have locked or whether the trailer is moving. Thus, for example, the power management module might, based upon feedback from the sensors, determine and set the first level of current to a maximum current that will avoid locking the electric brakes, thereby increasing braking effectiveness, and determine and set the second level of current to a minimum current sufficient to hold the trailer in place, thereby increasing power-use efficiency.
Additional modifications may be made to improve or enhance management or control of the current levels and durations in order to further maximize effectiveness and efficiency. For example, the power management module could be configured to deliver current to the electric brakes using a ramp or other linear or nonlinear transfer function to further avoid locking the electric brakes. Additionally, the power management module could be configured to control the first and second electric brakes differently or independently so as to, for example, maximize braking during the first duration and minimize current drain during the second duration. Additionally, the power management module could be configured to allow a user to adjustment the current levels and durations to account for such situation-specific factors as, for example, trailer load or road conditions. Additionally, the power management module could be configured to determine battery charge and other battery conditions and then manage current levels and durations to achieve the best effect. Relatedly, the power management module can be configured to provide a warning of impending brake release once battery power drops below a predetermined threshold.
Thus, it will be appreciated that the system of the present invention provides a number of substantial advantages over prior art emergency braking systems, including, for example, substantially improving both effectiveness and efficiency. These and other important aspects of the present invention are more fully described in the section entitled DETAILED DESCRIPTION, below.